Provided that the keys in your hash have a corresponding column name, you can add or remove keys at will, and this kind of code will work smoothly.

Update
Be aware that this solution won't work when the value submitted for update is a formula. E.g.
UPDATE wages SET salary = salary * 1.25 . If you pass "salary * 1.25" to a placeholder, you'll get a string, which MySQL tries to convert into a number, thus resulting in a value of "0" (zero). See the MySQL manual.
Remember that, since placeholders imply quoting, if you want to allow your users to use formulas you'll need to parse their input, check for allowed expressions, quote the quotable parts, and compose the query in a different way.

When putting a smiley right before a closing parenthesis, do you:

Use two parentheses: (Like this: :) )
Use one parenthesis: (Like this: :)
Reverse direction of the smiley: (Like this: (: )
Use angle/square brackets instead of parentheses
Use C-style commenting to set the smiley off from the closing parenthesis
Make the smiley a dunce: (:>
I disapprove of emoticons
Other